Path: csiph.com!aioe.org!bofh.it!news.nic.it!robomod From: Guenter Roeck Newsgroups: linux.kernel Subject: Re: Question about hwmon_attr_show_string Date: Tue, 07 Mar 2017 16:10:01 +0100 Message-ID: References: Dkim-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=roeck-us.net; s=default; h=Content-Transfer-Encoding:Content-Type: In-Reply-To:MIME-Version:Date:Message-ID:From:Cc:References:To:Subject:Sender :Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id:List-Help: List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=8TLEt/1wWfR3YmVo3ZUbAK6zsV3duppgHdX4+kNq5s8=; b=ZinTtYU2EZldb+nh9b+U8sKPY3 y6AmKubg0XKEnLY6DHlzn1ctRZF10eWqtPw+Z2N29NgdZ+0V0EJ2vdDGKWbuheZ/sqCcuTKekfYfy ByiIyBfn2jMwc8/wg0me1NpGPcFz3xl8cvZr+19qBUgHsgusShBX3G2bq4kwnHN2tX2WS/5y4ayc0 4PkNElSgbH5w7+6EyGlnLbTDTukU6onIzXMsfZmsRG03dFUsggSmbk5oN2IHFVIgPBUqtocCdsKvA A9NrfF3dh8fFfG8ZA3h6dy3rJjNRggsIiLP5MSB83jfA2sIsHbgktXTvPAt3bRzPEWmtfGDgLQ+5I cDcqjELw==; User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.5.1 MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit X-Authenticated_Sender: linux@roeck-us.net X-Outgoing-Spam-Status: No, score=-1.0 X-Antiabuse: This header was added to track abuse, please include it with any abuse report X-Antiabuse: Primary Hostname - bh-25.webhostbox.net X-Antiabuse: Original Domain - vger.kernel.org X-Antiabuse: Originator/Caller UID/GID - [47 12] / [47 12] X-Antiabuse: Sender Address Domain - roeck-us.net X-Get-Message-Sender-Via: bh-25.webhostbox.net: authenticated_id: linux@roeck-us.net X-Authenticated-Sender: bh-25.webhostbox.net: linux@roeck-us.net Sender: robomod@news.nic.it List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Approved: robomod@news.nic.it Lines: 65 Organization: linux.* mail to news gateway X-Original-Cc: =?UTF-8?Q?Peter_H=c3=bcwe?= , linux-hwmon@vger.kernel.org, linux-kernel@vger.kernel.org X-Original-Date: Tue, 7 Mar 2017 06:16:15 -0800 X-Original-Message-ID: <333a9a55-e6d3-97ed-6223-6d09cb5d3c03@roeck-us.net> X-Original-References: <201703030133.01363.PeterHuewe@gmx.de> <201703062148.36101.PeterHuewe@gmx.de> <20170306234755.GA16512@roeck-us.net> <20170307100846.0487135b@endymion> X-Original-Sender: linux-kernel-owner@vger.kernel.org Xref: csiph.com linux.kernel:1594322 On 03/07/2017 01:08 AM, Jean Delvare wrote: > Hi Guenter, > > On Mon, 6 Mar 2017 15:47:55 -0800, Guenter Roeck wrote: >> On Mon, Mar 06, 2017 at 09:48:35PM +0100, Peter Hüwe wrote: >>> Hi Guenter, >>> >>> I was wondering whether there was a particular reason why >>> hwmon_attr_show_string passes only an "empty" pointer(pointer) to the ops- >>>> read_string function rather than the buffer itself? >>> >>> Wouldn't this mean that in ops->read_string I'd have to reserve some space for >>> the value on the heap (and taking care to free it somewhere, since returning >>> an address on the stack is bad idea), instead of calling sprintf(buf, "%s\n", >>> s) directly? >>> >>> With the current implementation I have to sprintf it into my local buffer and >>> you sprintf it again into the final buffer. >> >> The idea was that the called code would return a pointer to a constant string, >> ie one that isn't changing from call to call. > > In that case, what about the following change? > > Subject: hwmon: Constify str parameter of hwmon_ops->read_string > > The read_string callback is supposed to retrieve a pointer to a > constant string. > > Signed-off-by: Jean Delvare Makes sense. I'll add it to -next. Thanks, Guenter > --- > drivers/hwmon/hwmon.c | 2 +- > include/linux/hwmon.h | 2 +- > 2 files changed, 2 insertions(+), 2 deletions(-) > > --- linux-4.10.orig/drivers/hwmon/hwmon.c 2017-02-19 23:34:00.000000000 +0100 > +++ linux-4.10/drivers/hwmon/hwmon.c 2017-03-07 08:22:27.784527968 +0100 > @@ -186,7 +186,7 @@ static ssize_t hwmon_attr_show_string(st > char *buf) > { > struct hwmon_device_attribute *hattr = to_hwmon_attr(devattr); > - char *s; > + const char *s; > int ret; > > ret = hattr->ops->read_string(dev, hattr->type, hattr->attr, > --- linux-4.10.orig/include/linux/hwmon.h 2017-02-19 23:34:00.000000000 +0100 > +++ linux-4.10/include/linux/hwmon.h 2017-03-07 08:21:28.247998585 +0100 > @@ -336,7 +336,7 @@ struct hwmon_ops { > int (*read)(struct device *dev, enum hwmon_sensor_types type, > u32 attr, int channel, long *val); > int (*read_string)(struct device *dev, enum hwmon_sensor_types type, > - u32 attr, int channel, char **str); > + u32 attr, int channel, const char **str); > int (*write)(struct device *dev, enum hwmon_sensor_types type, > u32 attr, int channel, long val); > }; > >